Method and device for closed-loop combustion control for an internal combustion engine

ABSTRACT

A method for closed-loop combustion control within an internal combustion engine, that includes, but is not limited to individual calculation of actual Start of Combustion (SoC) information for all cylinders of said internal combustion engine using information from a combustion sensor applied to the engine, calculation of 50% Mass Fraction Burned (MFB50) and SoC information using cylinder pressure sensor information available from at least one leading cylinder of the engine, using pressure-based MFB50 information from the at least one leading cylinder to control it in closed loop, and using pressure-based SoC information from said at least one leading cylinder as a reference value for comparison with the combustion sensor based value of SoC from the same cylinder in order to calculate the desired SoC for the other cylinders of the engine which are then controlled relative to said at least one leading cylinder.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to British Patent Application No.0915745.4, filed Sep. 9, 2009, which is incorporated herein by referencein its entirety.

TECHNICAL FIELD

The present invention relates to a method and a device for closed-loopcombustion control within an internal combustion engine.

BACKGROUND

It is known to control the injection of fuel into internal combustionengines using an open-loop control circuit. In these conventionalsystems the injection time and the pulse width of the injection aredetermined from predefined values stored in the engine's electroniccontrol unit. Although such systems exhibit acceptable performance, theyare otherwise prone to defects typical of open loop control. Forexample, the flow characteristics of an injector in a diesel engine maychange during time as a result of wear phenomena, thus the pulse widthused for the injector will no longer supply the engine with the desiredquantity of fuel, and in general the performance of the engine will bedegraded, giving way to higher emissions, higher fuel consumption,increased noise and even the possibility of damage to the engine.

In order to improve such situation, more recent engine combustionconcepts, for example diesel Premixed Charge Compression Ignition (PCCI)and gasoline Homogenous Charge Compression Ignition (HCCI), requireclosed-loop control of characteristic combustion parameters, such asStart-of-Combustion (SoC), 50% fuel mass fraction burned (MFB50),location of peak pressure (LPP) and other parameters, in order tostabilize combustion and reduce emission dispersion on acylinder-individual basis. Mostly combustion phasing based on MFB50 isperformed.

These parameters can be directly measured by means of combustionpressure sensors. These sensors are being developed for application inproduction engines in a configuration that uses one sensor per cylinder.

While this solution has the best control accuracy, one serious problemof this approach is the high cost of the pressure sensors and thereforealso sensor thrifting has been considered, e.g., having only twopressure sensors per engine or even one sensor per cylinder bank andapplying information derived from such pressure sensor(s) to controlalso the cylinder(s) without pressure sensor(s) in order to reduce totalcost. This second approach results in a reduced number of sensors perengine and gives way to closed-loop control of “lead cylinders” withpressure sensors and subordinated open-loop control of non-sensedcylinders depending on “lead cylinders”.

The benefit of this approach is reduced cost; the approach is stillacceptable for Euro5 emission control standard, but it has the drawbacksof limited controls quality, increased emission dispersion and ingeneral it is not acceptable for the tighter standard Euro6.

A further known approach is based on crank-speed fluctuation measuredwith a standard crank-speed sensor used to closed-loop controlcombustion phasing on a gasoline HCCI engine. Still another approachuses a torque sensor that provides a crank-angle resolved torque patternfor each cylinder. Torque is related to the in-cylinder pressure duringcombustion.

U.S. patent application US 2008/0053405 discloses another approach,namely a method of performing feedback control of the operation of aninternal combustion engine based on a signal obtained from a vibrationsensor and a crankshaft angle sensor. The vibration sensor preferablyused is a knock sensor traditionally applied in spark-ignition internalcombustion engines to detect auto-ignition. In the method a voltage orcharge signal from said vibration sensor is acquired multiple timesduring a window of engine rotation. These signals, after suitablefiltering and adjusting operation, are squared to obtain unfilteredenergy factor values which are low pass filtered to remove highfrequency components to obtain filtered energy factor values. A vectorof energy factors can be computed as a function of crank angle degreeover a particular window of engine rotation of interest. Based on theenergy factor vector, combustion phasing can be estimated. Such methodhowever mainly gives information on the start of combustion, because thevibration sensor substantially picks up vibrations associated with Startof Combustion (Soc) pulses for each cylinder.

At least one aim of the invention is therefore to provide for a methodand a device for closed-loop combustion control within an internalcombustion engine that improves the combustion phasing of the engine,while at the same time has reduced costs with respect to prior artmethods. A further aim of the invention is to provide a reliable methodfor closed-loop combustion control which does not require a powerfulhardware to be implemented. In addition, other aims, desirable features,and characteristics will become apparent from the subsequent summary anddetailed description, and the appended claims, taken in conjunction withthe accompanying drawings and this background.

SUMMARY

The embodiments of the invention provide for a method for closed-loopcombustion control within an internal combustion engine, wherein ofcomprising at least the following phases: individual calculation ofactual Start of Combustion (SoC) information for all cylinders of saidinternal combustion engine using information from a combustion sensorapplied to said engine; calculation of 50% Mass Fraction Burned (MFB50)and SoC information using cylinder pressure sensor information availablefrom at least one leading cylinder of the engine; using pressure-basedMFB50 information from said at least one leading cylinder to control itin closed loop; using pressure-based SoC information from said at leastone leading cylinder as a reference value for comparison with thecombustion sensor based value of SoC from the same cylinder in order tocalculate the desired SoC for the other cylinders of the engine whichare then controlled relative to said at least one leading cylinder.

The embodiments of the invention also provides for a device forclosed-loop combustion control within an internal combustion enginecomprising a combustion sensor applied to said engine and at least onepressure sensor applied to one of the cylinders of the engine, Thedevice comprises an electronic device for performing the calculations ofthe above described method.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and:

FIG. 1 is a schematic representation of the steps used for thecalculation of actual Start of Combustion (SoC) using raw data signalsfrom a applied to the engine;

FIG. 2 is a schematic representation of an internal combustion engineemploying the device for closed-loop combustion control according to oneembodiment of the invention; and

FIG. 3 is a schematic representation of a further embodiment of theinvention.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit application and uses. Furthermore, there is nointention to be bound by any theory presented in the precedingbackground or summary or the following detailed description.

A preferred embodiment of the present invention is now described withreference to FIG. 2 in which an engine block 16, having four cylinders10′-13′ is depicted, each cylinder being provided with its respectiveinjector 10-13. The engine block 16 has a combustion sensor applied toit. Preferably but not necessarily a vibration sensor is used, such as astandard “knock-sensor” device. Without loss of generality the termvibration sensor will be used in the following description, beingintended that in alternative other combustion sensors such as anionization sensor or a crankshaft wheel speed analysis may be usedequivalently for the aims of the invention. Pressure sensors 9 and 14are applied to only two of the cylinders and, in the exemplaryconfiguration depicted, pressure sensor 9 is applied to cylinder 13′while pressure sensor 14 is applied to cylinder 12′, the other twocylinders 10′-11′ being devoid of pressure sensors. Vibration andpressure sensors are connected to electronic processing means (notrepresented) for performing the calculations required by the method.

The first step in the method of the invention provides for an individualcalculation of actual Start of Combustion (SoC) information for allcylinders of the engine using information from the vibration sensor 15.In FIG. 2 block 8 represents the individual calculation of actual Startof Combustion (SoC) for cylinders 10′-13′ using data received fromvibration sensor 15. Such calculation may be performed through thefollowing SoC signal processing steps specified in FIG. 1:

First the raw signal 40 from the sensor 15 is bandpass filtered 41 toremove frequency components above and below certain values and then itis amplified; then the signal is rectified and subjected to amplitudeenvelope-shaping 42. Preferably the signal is acquired as function ofcrankshaft-angle 43 during a window 45 of engine rotation.

The Start of Combustion (SoC) pulse is detected by signal-comparisonwith a threshold 44, whereby the threshold can be either calibrated ordetermined real-time with respect to the peak-value of theamplitude-envelope. Finally linear scaling 46 between SoC detectionpulse occurrence and real-measured SoC is performed to determine actualSoC value 47. The actual SoC values for each cylinder 10′-13′ calculatedby block 8 are represented by numerals 22-25 in FIG. 2.

A further step of the method provides for the calculation of 50% massFraction Burned (MFB50) and SoC using cylinder pressure sensorinformation available from the pressure sensor 9 and 14, asschematically illustrated in blocks 3 and 7. The actual MFB50 forcylinders 13′ (pressure sensor 9) and (pressure sensor 14) arerespectively represented by numerals 18 and 20. Such pressure-basedMFB50 information is used to control in closed loop the respectivecylinders 13′ and 12′. Moreover, actual SoC values for cylinders 13′ and12′, respectively calculated from cylinder pressure sensors 9 and 14,are represented by numerals 19 and 21.

The next step of the method provides for the use of such pressure-basedSoC information from cylinders 13′ and 12′ as a reference value for thevibration sensor based SoC values for the same cylinders. Specificallyand with reference to FIG. 2, a comparison stage is provided in whichthe actual SoC 22 for cylinder 13′, calculated from data of thevibration sensor 15, is compared with actual SoC 19 calculated fromcylinder pressure sensor 9 and it is also fed to block 17 which performsthe calculation of desired Soc 26 for cylinder 10′. In the same way, theactual SoC 25 for cylinder 12′, calculated from data of the vibrationsensor 15, is compared with actual SoC 21 calculated from cylinderpressure sensor 14 and it is fed to block 17 which performs thecalculation of desired Soc 27 for cylinder 11′.

Finally the method provides for comparing the desired SoC values 26,27of cylinders 10′,11′ with actual SoC information 23,24 from the samecylinders in order to determine Start of Injection (SoI) for thosecylinders. Specifically, desired Soc 27 for cylinder 11′ is compared(block 5) with actual Soc 24 of cylinder 11′ derived from vibrationsensor in order to determine Start of Injection (SoI) for said cylinder.

At the same time, desired Soc 26 for cylinder 10′ is compared (block 4)with actual Soc 23 of cylinder 10′ derived from vibration sensor inorder to determine Start of Injection (SoI) for said cylinder. Theremaining cylinders 13′ and 12′ are controlled in a known way by meansof pressure sensors 9 and 14 respectively that derive actual MFB50 18and 20 and feed such values in order to be compared with (blocks 2 and6) a signal 1 that expresses a desired target MFB50.

Summarizing the method it is to be noted that MFB50 and SoC informationis calculated from cylinder pressure sensor information available fromone or two cylinders of the engine (in the example above the twocylinders 13′ and 12′) that work as a sort of “Lead Cylinders”.

Concurrently MFB50 is closed-loop controlled for the Lead-Cylinders asknown in the art. The pressure-based SoC values 22 and 25 of LeadCylinders form reference values for the vibration sensor based values ofSoC. The actual SoC of cylinder 13′ and 12′ are then compared withpressure-based SoC values 22 and 25 in order to calculate the desiredSoC for cylinders 10′ and 11′, which are then controlled relative to thelead cylinders. Consequently it is assumed, that by this procedure,MFB50 is closed-loop controlled for all cylinders as long asheat-release characteristics are equivalent.

A variant embodiment of the invention is depicted in FIG. 3, wherein thesame elements of the embodiment of FIG. 2 are represented with the samereference numbers. In this embodiment only one pressure sensor 9,applied to cylinder 13′, is provided for, the other three cylindersbeing devoid of pressure sensors. A vibration sensor 15 is also appliedto engine block 16, preferably but not necessarily a standard“knock-sensor” device.

Operation of the embodiment of FIG. 3 is similar to the one of FIG. 2,where actual SoC information is calculated individually for allcylinders from vibration sensor information. In parallel MFB50 and SoCinformation is calculated additionally from cylinder pressure sensor 9,cylinder 13′ working thus as “lead cylinder”. Concurrently MFB50 isclosed-loop controlled for the lead-cylinder 13′ as known in the art.The pressure-based SoC value 22 form a reference value for the vibrationsensor based values of SoC. The actual SoC 22 of cylinder 13′ is thencompared with pressure-based SoC value 19 in order to calculate thedesired SoC values 26-28 for the other three cylinders, which are thencontrolled relative to the lead cylinder 13′.

The invention has a number of important advantages over the prior art.For example, it allows the use of a low-cost combustion sensor forStart-of-Combustion (SoC) metric. As a second advantage, the inventionallows a precise closed-loop combustion phasing control with reducednumber of pressure sensors or even with only one pressure sensor perengine. Furthermore the invention does not need specially designedvibration sensors, because standard “knock-sensor” devices can beeffectively used, avoiding unnecessary costs. In general therefore theinvention allows a substantial reduction of costs with respect to theprior art, without a sensible degradation in the performance of theengine. Finally, the invention has a wide range of potentialapplications, for example in order to comply to Euro5 (and beyond)emission control standards. The invention is also equally applicableboth to diesel engines and to gasoline engines.

While the present invention has been described with respect to certainpreferred embodiments and particular applications, it is understood thatthe description set forth herein above is to be taken by way of exampleand not of limitation. Those skilled in the art will recognize variousmodifications to the particular embodiments are within the scope of theappended claims. Therefore, it is intended that the invention not belimited to the disclosed embodiments, but that it has the full scopepermitted by the language of the following claims. Moreover, while atleast one exemplary embodiment has been presented in the foregoingsummary and detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration in anyway. Rather, the foregoing summary and detailed description will providethose skilled in the art with a convenient road map for implementing anexemplary embodiment, it being understood that various changes may bemade in the function and arrangement of elements described in anexemplary embodiment without departing from the scope as set forth inthe appended claims and their legal equivalents.

What is claimed is:
 1. A method for closed-loop combustion control within an internal combustion engine, comprising the steps of: individually calculating of an actual Start of Combustion (SoC) for all cylinders of said internal combustion engine using information from a combustion sensor applied to the internal combustion engine; calculating a 50% Mass Fraction Burned (MFB50) and a SoC information using cylinder pressure sensor information available from at least one leading cylinder of the internal combustion engine; using a pressure-based MFB50 information from said at least one leading cylinder to control in a closed loop; and using a pressure-based SoC information from said at least one leading cylinder as a reference value for comparison with the combustion sensor based value of SoC from the same cylinder in order to calculate the desired SoC for the other cylinders of the engine which are then controlled relative to said at least one leading cylinder.
 2. The method for closed-loop combustion control as in claim 1, wherein the using of the calculating of MFB50 and Soc information using cylinder pressure sensor information available is performed in two leading cylinders of the engine.
 3. The method for closed-loop combustion control as in claim 1, further comprising using the pressure-based MFB50 information from two leading cylinders to respectively control in closed loop said cylinders.
 4. The method for closed-loop combustion control as in claim 1, further comprising using the pressure-based SoC information from two leading cylinders as a reference values for the combustion sensor based values of SoC.
 5. The method for closed-loop combustion control as in claim 1, wherein in respectively comparing the SoC values of two leading cylinders with pressure-based SoC information from said two cylinders in order to calculate the desired SoC for the other cylinders of the engine.
 6. The method for closed-loop combustion control as in claim 1, wherein the combustion sensor signal is acquired as function of crankshaft-angle during a window of engine rotation.
 7. The method for closed-loop combustion control as in claim 1, wherein said combustion sensor is a vibration sensor.
 8. The method for closed-loop combustion control as in claim 1, wherein the individual calculation of actual Start of Combustion (SoC) information for all cylinders of said internal combustion engine using information from a combustion sensor applied to said engine comprises the steps of: bandpass filtering of raw signal from said combustion sensor; rectifying and amplitude envelope-shaping of the signal; detecting of Start of Combustion (SoC) pulse by signal-comparison with a threshold, whereby the threshold can be either calibrated or determined real-time with respect to the peak-value of an amplitude-envelope; and linear scaling between SoC detection pulse occurrence and real-measured SoC.
 9. A device for closed-loop combustion control within an internal combustion engine having a plurality of cylinders, comprising: a combustion sensor applied to the internal combustion engine; a pressure sensor applied to at least one of the cylinders of the engine; and an electronic device adapted to: individually calculate an actual Start of Combustion (SoC) for all cylinders of said internal combustion engine using information from a combustion sensor applied to the internal combustion engine; calculate a 50% Mass Fraction Burned (MFB50) and a SoC information using cylinder pressure sensor information available from at least one leading cylinder of the internal combustion engine; use a pressure-based MFB50 information from said at least one leading cylinder to control in a closed loop; and use a pressure-based SoC information from said at least one leading cylinder as a reference value for comparison with the combustion sensor based value of SoC from the same cylinder in order to calculate the desired SoC for the other cylinders of the engine which are then controlled relative to said at least one leading cylinder.
 10. The device for closed-loop combustion control as in claim 9, further comprising at least two pressure sensors, each of the at least two pressure sensors applied to a cylinder of the internal combustion engine.
 11. The device for closed-loop combustion control as in claim 9, wherein said combustion sensor is a vibration sensor.
 12. The device for closed-loop combustion control as in claim 11, wherein said vibration sensor is a knock sensor.
 13. The device for closed-loop combustion control as in claim 9, wherein the use of the MFB50 and Soc information using cylinder pressure sensor information available is performed in two leading cylinders of the engine.
 14. The device for closed-loop combustion control as in claim 9, said electronic device further adapted to use the pressure-based MFB50 information from two leading cylinders to respectively control in closed loop said cylinders.
 15. The device for closed-loop combustion control as in claim 9, said electronic device further adapted to use the pressure-based SoC information from two leading cylinders as a reference values for the combustion sensor based values of SoC.
 16. The device for closed-loop combustion control as in claim 9, wherein in respectively comparing the SoC values of two leading cylinders with pressure-based SoC information from said two cylinders in order to calculate the desired SoC for the other cylinders of the internal combustion engine.
 17. The device for closed-loop combustion control as in claim 9, wherein the combustion sensor signal is acquired as function of crankshaft-angle during a window of engine rotation.
 18. The device for closed-loop combustion control as in claim 9, wherein said combustion sensor is a vibration sensor.
 19. The device for closed-loop combustion control as in claim 9, wherein said electronic device is adapted to perform the individual calculation of actual Start of Combustion (SoC) information for all cylinders of said internal combustion engine using information from a combustion sensor applied to said internal combustion engine by: bandpass filtering of raw signal from said combustion sensor; rectifying and amplitude envelope-shaping of the signal; detecting of Start of Combustion (SoC) pulse by signal-comparison with a threshold, whereby the threshold can be either calibrated or determined real-time with respect to the peak-value of an amplitude-envelope; and linear scaling between SoC detection pulse occurrence and real-measured SoC. 